1) Technical Field
This invention is concerned with a portable apparatus and method for diagnosing truck and trailer axle alignment and determining desired axle adjustments.
2) Background Information
The tractor as well as the trailer in a tractor-trailer vehicle combination often have a problem maintaining axle alignment. The problem results from the axles not being perpendicular to the fore-and-aft centerline of the frame of the tractor, as well as the trailer axles not being perpendicular to the trailer frame centerline. Also, the axles are generally not parallel and two adjacent tractor drive axles, or two adjacent trailer drag axles, have a tandem scrub angle when misaligned relative to each other.
These problems result in excessive tire wear, a reduction in fuel economy and driver fatigue.
The highest operating expense next to operator salaries and fuel costs for class 7 and 8 vehicles is the tire related expense. The Maintenance Practices Council for the American Trucking Association of Alexandria, Virginia publishes the recommended maintenance practice "RP-207" for periodic axle alignment verification. This recommended practice defines the desired relationships for proper axle alignment to maintain parallelism along with proper thrust line and drag line orientation.
A system for checking truck or trailer axle parallelism by a means for projecting the centerline of the axle end portion to a real or imaginary reference surface, using an apparatus attached to each wheel, is common in the trucking industry. Various manufacturers provide systems and apparatus including Hunter Engineering Co. of Bridgeton, Miss. Kansas Jack, Inc. of McPherson, Kans. Bee Line Company of Bettendorf, Iowa, Axle-Tru, Inc. of Columbia City, Ind., Bear Automotive Service Equipment Company of Milwaukee, Wis. and Meyers Tire Supply of Akron, Ohio. These systems and components have varying degrees of complexity and size. Most systems are used by specialty service companies and are not portable or cost effective systems for a trucking fleet or the field service personnel of truck and tire manufacturers. One apparatus which is somewhat portable is the Fiaky apparatus shown in FIG. 1. This device 10, to define the axle centerline and project it to a location on a reference surface 8, is distributed by M. Muller and Company of Paris, France. The disadvantage to this apparatus is that multiple devices 10 are required to locate each axle being investigated. Also then end 40 of the axle 6 has a location 42 on the reference surface 8 which is axially interior to the tire 4 requiring the vehicle to be moved to identify this location 42.
Examples of sophisticated electronic systems and apparatus are disclosed in the U.S. Pat. No. 4,629,317, U.S. Pat. No. 4,337,581 and FR 2467385. Electronic devices include light emitters, reflector devices and receivers or tagets. They combine sensor signals to measure and display specific alignment parameters using a common geometric reference, such as the vehicle body centerline and the wheel axis of rotation. A typical problem with electronic devices is the relative ease with which a beam of light can deviate from a perpendicular relationship to its support and consequently the wheel axle centerline.
Various means for computing and displaying axle alignment parameters are disclosed in the U.S. Pat. No. 4,319,838, U.S. Pat. No. 4,381,548, and U.S. Pat. No. 4,898,464. A computer is easily programmed to store axial alignment parameters, vehicle suspension geometry and the adjustments possible for each type of suspension system available from manufacturers. The computer calculates the relative position of axles from relative distances between locations at axle end portions in U.S. Pat. No. 4,381,548. Computations can either be online from electronic signals fed directly to the control microprocessor and CRT display (U.S. Pat. No. 4,898,464) or offline by keying dimensions into the computer and providing a graphical display on a monitor, as used in this invention.
Means for supporting alignment devices at the wheel of the vehicle are disclosed in the U.S. Pat. No. 3,181,248, U.S. Pat. No. 4,115,926, U.S. Pat. No. 4,239,389, U.S. Pat. No. 4,337,581, U.S. Pat. No. 4,854,702 and FR 2562658. The mechanical device of U.S. Pat. No. 3,181,248 includes interconnections between wheels transversely and longitudinal. This device would not be very portable. Numerous support means (U.S. Pat. No. 4,239,389, U.S. Pat. No. 4,337,581, U.S. Pat. No. 4,854,702 and FR 2562658) have wheel rim contact devices. A support means contacting the wheel rim must be independent of any deviations of the wheel from a true plane of the wheel rotation whereby mechanical tolerances in the wheel, as well as in the instrumentation components, must be accounted for without interferences in the measured results. The U.S. Pat. No. 4,115,926 has a magnetic mounting clamp 17 which remains aligned with the wheel axis extension. This clamp is used for toe adjustments of the front wheel of an automotive vehicle and would not be appropriate for the wheels of a truck. Any modification for use on trucks would not be easily portable and a different clamp would be necessary for steering, drive and trailer axles.
U.S. Pat. No. 4,239,389, U.S. Pat. No. 4,319,838 and U.S. Pat. No. 4,854,702 cited previously disclose a spirit level or bubble device to position and associated part of the support means in a horizontal plane. The primary purpose of these leveling devices is to allow for radial runout and to nullify physical inaccuracies of wheel rims in the adjustment systems.
U.S. Pat. No. 4,239,389 and FR 2562658 cited previously disclose the use of a rod approximately perpendicular to the plane of the wheel. These rods are adjusted to become coextensive with the vehicle axle centerline in a horizontal plane or perpendicular to the wheel plane of rotation. These rods are not necessarily collinear or parallel with the axle centerline.
An alignment of the vehicle thrust line effect of a nonsteerable wheel, or pair of wheels associated with one drive axle, is discussed in the U.S. Pat. No. 4,341,468 and U.S. Pat. No. 4,942,667. A combination of an electronic device 12 and a mechanical frame 22 with centering elements 28 and 30 is disclosed for aligning the axles of a tractor or trailer in U.S. Pat. No. 4,942,667. Axles become misaligned due to bends, bows, twists and other irregularities in vehicle frames as well as assembly tolerances in the suspension system during manufacture. The centering elements of this patent are not precision devices for accurate axle centerline projections and the system is not very portable. In addition, there is no disclosure for making drive axles parallel by using this system, and doing this is not obvious.